Update on Perth River Valley Work Programme – 7 June 2019

This operation is part of a wider programme of research and development that seeks to develop cost-effective tools and techniques to completely remove possums and, potentially, rats, from large mainland areas, and prevent these predators from re-establishing. If this work is successful, it will have significant benefits for the many native species that live in the Perth River valley, and will mean that it is no longer necessary to use landscape-scale aerial 1080 to control predators in the valley.

Detecting possums, rats and stoats after the first phase of the operation

Our network of 142 lured trail cameras has enabled us to keep an eye on predator abundance in the operational area for several months. Before the first phase of the operation, 98% of cameras detected a possum; 65% detected a rat; and 36% detected a stoat. These detections represent an estimated starting population of 8,000-20,000 possums; 3,500-9,000 rats; and 20-40 stoats across the Perth River valley research area.

In the month since we completed the first phase of the operation, only 7 cameras have detected a possum; 1 has detected a rat; and 9 have detected a stoat. Based on these detections, our team has begun modelling the remaining population of possums, rats and stoats. Our initial estimates range from 13-35 possums; 5-15 rats; and 1-3 stoats across the research area. Our most recent camera data indicates have all three stoats have since died from secondary poisoning.

This is an excellent result for an aerial 1080 operation, which we think reflects (i) the benefits of two rounds of prefeeding, (ii) the careful attention to applying a consistent coverage of bait across the entire operational area, and (iii) the ideal weather conditions, with toxic baiting followed by 6 dry nights.

We are also continuing to search for any predators that survived the first phase of the operation, and we are using the results to help ensure the predator removal is successful. To do this, we’ll use the same network of 142 cameras, reinforced with a much larger number of chew cards.

Kea in the Perth River valley

Toxicology testing has confirmed that two of the 13 radio-tagged kea in the Perth River valley died after eating 1080 bait during the first phase of the predator removal operation.

The other 11 radio-tagged kea are all alive. We are also pleased to report that none of the adult female kea in the radio-tagged population died during the operation. This is an important outcome for kea in the area, because adult female kea are most vulnerable to predation, given their ground-nesting habits and extended nesting cycle[1].

Our team has frequently sighted kea in the Perth River valley since the first phase of the operation was carried out, both in person and via camera footage from our detection network (including the cheeky trio below).

We anticipate that the removal of possums and rats, and the work to control stoats to very low numbers, will have significant benefits not only for kea, but for many of the treasured native species that live in the Perth River valley, including rock wren, whio and rata.

For more information, please email us at info@zip.org.nz.

[1] Kemp JR, Mosen C, Elliott GP, Hunter CM. (2018). The effects of aerial poisoning for pest mammal control on the productivity of the kea (Nestor notabilis). New Zealand Journal of Ecology 42.